This invention relates to processes and treating solutions for impregnating wood at elevated pressures with impregnants such as preservatives and fire retardants in a liquid carrier which is subsequently evaporated from the wood. In particular, the invention relates to processes and treating solutions for impregnating wood with pentachlorophenol contained in an aliphatic hydrocarbon or halogenated aliphatic hydrocarbon liquid carrier which boils below 130.degree. C. at ambient atmospheric pressure and readily liquefies at ambient atmospheric temperatures when placed under elevated pressure.
Traditionally, wood has been impregnated with creosote and more recently with a solution of pentachlorophenol and oil to preserve the wood against fungus, insects, and the like. Additionally, such solutions when impregnated into wood, especially utility poles, serve as a lubricant so that projectiles such as, for example, nails, climbing irons and the like easily penetrate the wood when pressure is applied against the projectiles.
Within the last 15 years pressure treatment processes for wood have emerged wherein the liquid carrier for the impregnant is evaporated from the treated wood. These processes involve impregnating wood at an elevated pressure with a treating solution containing an impregnant such as a preservative or fire retardant in a liquid carrier such as an aliphatic hydrocarbon. These liquid carriers are liquid at wood impregnating conditions of elevated pressure but boil at a temperature below 130.degree. C. at ambient pressure and, therefore, may be removed from the treated wood by evaporation.
In addition, the treating solution may contain a cosolvent for the impregnant which also is soluble in the liquid carrier. Examples of these types of processes are described in U.S. Pat. Nos. 3,199,211 and 3,200,003 and Canadian Pat. No. 863,885.
The elevated pressure wood treating processes wherein the liquid carrier is evaporated from the treated wood produces a treated wood that does not possess internal lubrication like that present in creosote treated wood. Consequently, the treated wood from such elevated pressure wood treating processes is more resistant to penetration with projectiles. When the treated wood is a utility pole, a considerable effort is required by linemen to insert the spur of their climbing iron into the pole. If the spur does not penetrate the pole to a safe depth the lineman would not have ample support, thereby increasing the hazards of pole climbing.
It is an object of this invention to provide a process and treating solution to produce wood from a pressure impregnation treatment that allows for improved penetration of projectiles without deleteriously affecting the efficacy of the impregnant in the wood or the benefits of the pressure treatment.